1. Field of the Invention
The present invention relates to a multi-lobal hollow filament having stiffening ribs in the core portion and at least one transverse web in each lobe, and to a spinneret plate for producing the filament.
2. Description of the Prior Art
Fibers useful for carpet manufacture exhibit certain desirable performance criteria. These criteria include good crush resistance, high cover and good soil hiding ability. The structure of the fiber is a determinative factor in the ability of a given fiber to meet these performance criteria.
The crush resistance of a carpet depends on the stability properties of the pile fibers used in the carpet. The higher the stability of the fiber, the more resistant to crushing is the carpet. The covering ability of a carpet is determined by the space occupied by the fiber cross-section. For a given crimp a measure of the space occupancy for a lobal fiber is given by the fiber""s modification ratio. The higher the modification ratio of the fiber, the greater the covering ability of the carpet.
The presence of hollow regions in the interior of the fiber further increases the covering power and simultaneously increases its light scattering ability and decreases its luster. Thus, the presence of hollow regions coupled with the modification ratio, determine the fiber""s covering and soil hiding ability. U.S. Pat. No. 5,380,592 (Tung) and European Patent Office Publication 661,391 disclose a trilobal or tetralobal filament having a hollow core portion and an axially extending void in each lobe.
In another aspect hollow fibers with the same modification ratio and surface area as against solid fibers reduce the specific gravity according to the percentage of the fiber that is hollow. For example, a twenty percent hollow (or xe2x80x9cvoidxe2x80x9d) ratio reduces the specific gravity or density for nylon fibers from 1.14 to 0.91 grams per cubic centimeter and reduces the specific gravity for polyester fibers from 1.35 to 1.08 grams per cubic centimeter (both twenty percent reductions). This is desirable for lightweight carpets, apparel or fabrics.
Designing the structure of the fiber to enhance one of these performance criteria is often detrimental to another performance criterion. For example, in U.S. Pat. No. 5,208,107 (Yeh et al.), a multi-lobal synthetic fiber has a single axially extending central void. Although this structure may enhance the fiber""s stability it is not well-suited to enhance the soil hiding ability of the fiber.
As another example, U.S. Pat. No. 4,770,938 (Peterson et al.) shows a trilobal fiber having elongated voids extending through each lobe. Although such a structure increases the soil hiding capability of the fiber the lack of rigidity makes the lobes prone to collapse, thus detracting from the crush resistance of the fiber. If the structure of the lobes were rigidified as in U.S. Pat. No. 5,322,736 (Boyle et al.) the fiber becomes more crush resistant, at the cost of increased polymer.
In view of the foregoing, it is believed advantageous to provide a multi-lobal fiber structure that optimizes the fiber""s soil hiding and covering ability, without sacrificing crush resistance and without increasing the volume of the polymer material in the fiber.
The present invention is directed to a thermoplastic synthetic polymer filament comprising a core portion having a number N lobes joined thereto. Preferably, three or four. lobes may be provided, thereby respectively defining trilobal and tetralobal filament configurations. Each lobe has a tip thereon and is joined to the core portion along an inscribing circle. The filament has a central axis extending therethrough. N stiffening ribs are formed in the core portion, with the ribs extending radially inwardly toward the axis of the filament. The stiffening ribs cooperate to define at least N hollow regions in the core portion. Each hollow region in the core aligns radially with a respective lobe.
In one embodiment the radially inner ends of the stiffening ribs may be spaced from each other and from the central axis of the filament, thereby to define passages within the core portion through which the hollow regions communicate with each other. Alternatively, each stiffening rib may extend to meet and join to the other of the ribs along the axis of the filament whereby the hollow regions in the core portion are isolated from each other. The ribs in the core portion form abutting members on the interior of the filament that contact with each other under high face loading to enhance the stiffness and load capacity of the filament.
Each lobe has at least one opening disposed between the tip of the lobe and the inscribing circle. The opening in each lobe and the hollow region of the core portion corresponding to that lobe cooperate to define a transverse stiffening web across each lobe. The presence of the transverse stiffening web across each lobe prevent the lobe lateral edges from being deformed towards the exterior of the filament, resulting in a high degree of rigidity and crush resistance.
In accordance with another modified embodiment each lobe may be provided with a second opening therein so that the first and the second openings cooperate to define a second transverse web extending across the lobe. When provided the second opening in each lobe is disposed between the first opening and the tip of the lobe.
In yet another embodiment the major portion of each lateral edge of each lobe may be substantially linear over substantially its entire length. The arm angle for linear edge filament lies in the range from about zero to about fifteen degrees. Alternatively, the major portion of each lateral edge is convexly curved over substantially its entire length.
Any filament in accordance with any of the various embodiments of the invention illustrated herein has a modification ratio that lies in the range from about 1.6 to about 4.0, and preferably in the range from about 2.0 to 3.0, and most preferably in the range from about 2.3 to about 2.6. The filaments have a total void percentage in the range from about seven (7%) to about thirty percent (30%), and more preferably, in the range from about twelve (12%) to about twenty-two percent (22%).
In another aspect the present invention is directed to a spinneret plate for producing any of the thermoplastic synthetic polymer filaments summarized above. The spinneret plate comprises a cluster of N pairs of peripheral slot segments centered about a central point. To form lobes having substantially linear or convexly curved lateral edges, the peripheral slot segments are either substantially linear or convexly curved, respectively.
Each peripheral slot segment in each pair is joined to an adjacent peripheral slot segment at a junction point. A rib-forming slot extends radially inwardly from each junction point toward the central point of the cluster. The distance between the junction point and the central point of the cluster occupied by each rib-forming slot determines whether the ribs meet at the axis or whether the inner ends of the ribs are spaced from the axis.
Each slot segment in each pair is confrontationally disposed with respect to a slot segment in another pair. At least one web-forming slot extends from each peripheral slot segment toward the peripheral slot segment with which it is confrontationally disposed. If desired, a second web-forming slot may also extend from each peripheral slot segment toward the confrontationally disposed peripheral slot segment.